The only people i know who have thermal issues are ones who try to run lipo rx packs with no regulators or improper servo settings. I run the 603FF on 7.4v lipo with a 6.5V 5A regulator OUTSIDE the rx box. No issues what so ever. Also a lot of people don't take the time to set up their end points as precisely as needed, which in turn generates strain and heat.
I have the 3PM-MX, it has been a perfectly flawless system. I bought it after driving my friends rig with a 3PK with a 603FS rx on the same lipo and reg. I dropped Spektrum after 6 years of use and never looked back.